Pit prop and the like



June 28, 1949. R. G. CABLE 2,474,464

PIT-PROP AND THE LIKE Filed April 14, 1948 2 Sheets-Sheet l |ii INVENTOR.

June 28, 1949. R. G. CABLE 7 2,474,464 I PIT-PROP AND THE LIKE Filed April 14, 1948 2 Sheets-Sheet 2 IN VEN TOR.

Patented June 28, 1949 UNITED STATES PATENT OFFICE PIT PROP AND THE LIKE Application April 14, 1948, Serial No. 21,023 In Great Britain April 24, 1947 Claims.

This invention relates to props and more especially to pit-props.

Ah object of the invention is to provide a prop which can easily be assembled in position e. g. in a mine, in such manner that the prop makes adequate contact with the supporting surface and the superimposed load.

According to the invention a prop comprises two relatively movable portions and means for admitting liquid under pressure to move said relatively movable portions apart and thus adjust the overall height of the prop.

Known pit-props, whether of timber or metal, are rigid members of fixed length and consequently, upon relative movement of the floor and roof in a mine towards one another, the props either break or bend. When the floor and roof surfaces are good firm surfaces such relative movement of the floor and roof may be permitted to some extent. But such movement may often be of such an extent as would cause the known timber or metal props to break or to bend, to such degree that their load supporting capacities are seriously impaired.

A further object of the invention is to provide an improved prop which will still possess adequate supporting capacity even after a substantial movement of the surfaces on which it bears has occurred.

The invention accordingly provides a prop which is collapsable when the load thereon exceeds a predetermined value while maintaining its load carrying capacity substantially unimpaired during variation of the height of the strut under such load.

The invention further provides a prop which comprises means for permitting some of the liquid to escape from the cylinder when the load on the prop exceeds a predetermined value and thereby enable the Height of the prop to be decreased under the influence of the load.

The invention further consists in a prop which comprises a portion adapted to rest on a load supporting surface, a further portion adapted to bear against a superimposed load, a cylinder connected with one of said portions, a piston connected with the other of said portions, a nonreturn inlet valve for admitting liquid under pressure to the cylinder whereby the two first-mentioned portions may be forced against the supporting surface and the load respectively and valve means for permitting liquid to escape from the cylinder when the load on the prop exceeds a predetermined value and thereby cause the height 55 2 of the prop to be adjusted in dependence on the load on the prop.

The invention will be described by way of example with reference to the accompanying drawings of a pit-prop and in which Fig. 1 is a part sectional elevation.

Fig. 2 is a part sectional elevation on the line A-A of Fig. 1.

Fig. 3 is an elevation on a smaller scale of the pit-prop shown in Figs. 1 and 2.

Fig. 4 is a fragmentary section on a larger scale of a part of Fig. 1 showing the inlet valve and Fig. 5 is a, fragmentary section on a larger scale of a part of Fig. 2 showing the bleeder or escape valve.

Referring to the drawings, the pit-prop comprises a column I of which the upper portion is formed by a cylinder 2, and upper block 3 which is in screw-threaded engagement with the cylinder 2. The lower portion of the column I is formed by a piston 4 into the lower end of which is screwed a foot 5. The under surface of the foot 5 is dished as shown.

To the lower edge of the cylinder 2 is screwed a collar 6 and fixed to this collar by bolts 6a is a further collar 1. Between the two collars 6 and 7 is a packing ring of suitable material, for example, leather, which makes a tight fit on the piston 4 while permitting relative movement between the cylinder and piston to take place. The inner surface of the cylinder 2 and the outer surface of the piston 4 are stepped at 8 so that upward movement of the cylinder relative to the piston is limited. The head 9 of the piston is formed by a block I'D which is screwed to the piston barrel and to this head 9 a cup leather II is clamped by bolts l2 and a washer is. The upper block 3 comprises a chamber l 4 which is open to the interior of the cylinder 2. Into the chamber [4 opens a valve controlled duct 15 through which liquid under pressure is admitted to the chamber l4 and thence to the cylinder. A non-return inlet valve 16 (see particularly Fig. 4) is provided to admit liquid to the cylinder and to prevent es cape of the liquid therefrom via this valve. The valve 16 comprises a valve member I! which is urged by a spring I 8 against a seating l 9 formed in a valve body 29, in the direction to close the valve. A screw-threaded pipe connection 2| is provided to receive a pipe-fitting for connection with a source of liquid under pressure. The outer surface of the block 3 is recessed to receive the valve l6 which is secured-to the block by studs 22. Seals 23 and 24, suitably leather washers, are

3 provided to make liquid tight joints between the valve body and the block 3.

In order that the overall height of the prop may be reduced when relative movement occurs in a mine between the roof and floor or should the load on the prop increase for some other reason and the liquid pressure in the cylinder 2 thus be increased beyond a predetermined value, a bleeder valve is arranged in the block 3.

The bleeder valve 25 (see particularly Fig. 5) comprises a valve body plug 26 which is provided with a bore in which the stem of a valve member 28 is movable. The head of the valve member 28 is located in a valve chamber 29 in the valve body 30 and is urged by a spring 31 towards a valve seating 32 in the valve body, 30. The valve body plug 26 is also provided with a number of ducts 33 of small bore to permit of escape of liquid from the cylinder via the valve chamber 29 when the pressure in the cylinder 2 exceeds the predetermined value and the head of the valve member 28 is forced from the seating 32 against the action of the spring 3i. The wall of the valve chamber 29 abuts against a seal 34 suitably a leather washer, which is interposed between the inner surface of a recess formed in the block 3 to receive the valve 25 and the outer wall of the valve chamber 29. A further seal 35 e. g. a, leather washer, is provided between a further surface in the'r'ecess in the block 3 and the valve body 30. The valve 25 is secured to the block 3 by studs 36. Adjustment of the pressure at which the bleeder valve 25 permits liquid to escape from the cylinder 2 is effected by screwing or unscrewing the valve body plug 26 in the valve body 30 so as to vary the compression of the spring 3|.

The upper part of the block 3 is recessed to form a socket in which is mounted a ball member 3'1. Fixed to the ball member 37 by studs 38 is a short joist 39. The block 3 is formed with upstanding ears or flanges 40 between which the ball member 31 is located and held by a pin 4| which passes through the ears 40 and ball member 31. The arrangement is such that the ball member 3'! is movable on the surface of the socket in the block 3 so that the joist 33 may accommodate itself to the slope of a mine roof. In the construction shown to the drawings the joist 39 forms part of the head of the prop but it will be understood that the joist itself may be absent if it is so desired.

The foot 5 may also be pivotally mounted to the piston 4 if desired while the under-surface of the foot, and also the upper surface of the head, may be serrated or otherwise roughened.

The adjustment of the bleeder valve 25 may be so effected that liquid is permitted to escape from the cylinder before the head or foot of the prop is forced into the roof or floor so as to break up the surface adjacent the supporting surfaces of the prop or at least the tendency of the prop to efiect such damage of the roof or floor may be reduced by suitable adjustment of the setting of the bleeder valve.

An objection which has been made against metal pit-props was that they do not, as do timber props, give audible warning of the fact that a squeeze is occurring, i. e. that relative movement between the roof and floor is proceeding. When the prop provided by the invention is arranged so that liquid is allowed to escape from the bleeder valve to the exterior of the prop, the appearance of this liquid will indicate that a squeeze is occurring and the liquid may be .4 suitably coloured so that its appearance is made more easily recognisable.

It will, of course, be clear that the liquid escaping through the bleeder valve may be caused to flow to a suitable receptacle.

It will be appreciated that the .piston may be attached to the head of the prop and the cylinder to the foot.

It will further be appreciated that the prop provided by the invention may be removed when desired, the supply of liquid to the prop first having been interrupted and the bleeder valve opened to release the pressure in the cylinder; The prop may then be collapsed and removed for use at a different site. The prop is consequently recoverable for further use to a degree greater than was hitherto possible.

The prop may be made of any suitable material, e. g. an aluminium alloy. In this case the bearing surfaces of the piston and cylinder may be given a hard bearing surface by a hard chrome coating formed on these surfaces.

In a modification the joist 39 may be connected rigidly to the block 4.

I claim:

1. A prop which comprises a portion adapted to rest on a load supporting surface, a further portion adapted to bear against a superimposed load, a cylinder connected with one of said portions, a piston connected with the other of said portions, a non-return inlet valve for admitting liquid under pressure to the cylinder whereby the two first-mentioned portions may be, forced against the supporting surface and the loads respectively and valve means for permitting liquid to escape from the cylinder when. the load on the prop exceeds a predetermined value and thereby cause the height of the prop to be adjusted in dependence on the load on the prop.

2. A prop which comprises a cylinder connected with one end of the prop, a piston connected with the other end of the prop, valve means for admitting liquid under pressure to the cylinder whereby the overall length of the prop may be adjusted and valve means adapted to \permit liquid to escape from the cylinder when the pressure on the prop exceeds a, predetermined value, the arrangement being such that liquid which has escaped from the cylinder is visible on the exterior of the prop.

3. A prop which comprises a portion adapted to rest on a load supporting surface, a portion pivotally mounted at the top of the prop and adapted to bear against a'surface opposite to the load supporting surface, a cylinder connected with one of said portions, a piston connected with the other of said portions, a non-return inlet valve for admitting liquid under pressure to the cylinder whereby the two first mentioned portions may be forced respectively against the said load supporting surface and the said opposite surface and valve means for permitting liquid to escape from the cylinder when the load on the prop exceeds a predetermined value and thereby cause the height of the prop to be adjusted in dependence on the load on the prop.

4. A prop having opposite end portions, a member pivotally attached by a ball and socket joint to and extending beyond one of said end portions, a cylinder connected with one or said end portions, a piston connected with the other of said end portions, a non-return valve for admitting liquid under pressure to the c linder whereby the two end portions may be forced apart to'extend the prop against opposite surfaces and valve means for permitting liquid to escape from the cylinder when the load on the REFERENCES CITED prop exceeds a predetermined value and thereby The following references are of record in the cause the height or the prop to be adjusted in file of this patent: dependence on the load on the prop. 5

5. A prop as claimed in claim 1 which com- UNITED STATES PATENTS prises manually operable means adapted to ac- Number Name Date tuate the valve means for permitting liquid to 752,201 hri nsen Feb- 19 4 escape from the cylinder. 1,418,336 Stage June 6, 1922 RICHARD GEORGE CABLE. 10 1,744,673 Pomeror Jan. 21, 1 

